Quick and easy personal evaporative cooler

This quick and easy evaporative cooler might be just the thing the next time the air conditioning goes on the fritz. [Stephen] saw an eBay listing for a personal air conditioner that used a moist sponge and fan to send some cool relief your way. But he wanted to run his own test to see if it really did anything before laying down the cash.

The idea is to run air past a moisture source. Some of the heat energy in the air is reduced through evaporation resulting in the exhaust air feeling a bit cooler. It’s the same concept used in swamp coolers (an evaporative type of air conditioning). To build his device [Stephen] grabbed a refrigerator deodorizer which uses a hinged plastic cage to hold a packet of baking soda. He attached a small PC fan to the cage, then inserted a damp sponge. This is so easy to put together you could hit the dollar store on your lunch break and have some relief for the second half of the work day.

In Ohio, or a lot of other places in the summertime, you’re right: The humidity is usually so high on a hot day that it won’t work at all. (Phase-change, compressor-based cooling systems are common in these parts.)

In the desert, or any other dry climate: Works fine. The extra humidity might even be a plus. (Swamp coolers are common in these parts.)

Different methods for different environments. And if it’s working where he’s at, then it’s a good hack. *shrug*

I’ve got the commercial version of this. The same one he mentions in the video. It works very well, especially in areas that aren’t inherently high in humidity. I was wondering how I could make a little DIY version, it seemed like a lot of work. But this is an ingeniously simple way to do it.

I helped my kids make something similar to this after reading up on the cost efficiency of swamp coolers over aircon. We just used plastic food containers and hacked away at those foam hand fans. As long as you’re not inside a 2ft cardboard box where the humidity might build up quickly then it will continue to cool you down throughout the day. If you don’t have a sponge then any old fabric scraps can also be used. Dip them in water with ice cubes, even cooler!

Ice on the other hand absorbs 333 kJ/kg of heat and water absorbs 4.19 kJ/kg/K, which means that freezing and then melting a gallon of water to room temperature gives you 440 Watts of cooling power for one hour.

To match the 9000 BTU/h AC unit, you would need to melt a cubic foot of ice every 1½ hours.

Interestingly, one could use a (slightly modified) 9000 BTU/h AC unit and produce a cubic foot of ice every 1.5 hours, or a ton of it every 30 hours, which can then be transported somewhere else in order to cool something remotely.

This is the basis for the somewhat lesser-used (these days) term of describing air conditioning capacity in terms of tons, as in tons-per-day of ice that it can produce.

A ton of ice is commonly accepted to require about 288,000 BTU to produce. Divide that by 24 hours, and it takes a 12,000 BTU/h unit to produce a ton of ice in a day. Extrapolate simply, and a 9,000 BTU/h unit can produce 3/4 ton of ice per day, or a ton in 1.25 days.

Amusingly, this also means that it would take 3/4 ton of ice — per day — to match the cooling capacity of a not-so-huge 9,000 BTU/h air conditioner.running at maximum capacity.

It doesn’t really work like that because the CoP of the AC unit changes when you change the outlet temperature. The larger the difference, the less powerful the unit, so if it’s designed to make 70 F out of 100 F and you want it to make 32 F, it won’t pump as much heat – or in practical terms, it won’t pump as much air or water.

Of course if you cool it down with air that’s already 62 F then it should work the same because the temperature difference is the same. Trouble is, if it’s 62 F outside you don’t need an AC unit.

Heat pumps work like that. They pump the most heat per input power when there’s 0 degrees difference between input and output. It’s just like running a water pump – the higher you lift the pipe, the less water goes through.

Get a couple of old Socket 7 CPU coolers, big ones made for the later, faster CPUs. Run some paracord between the fins, connect with a clasp, lash the lot around your neck with one cooler on either side.

Just the aluminum heatsinks alone will feel really cold, but eventually they’ll warm up. Hook up the fans to a battery pack and it’ll feel like you’ve strapped ice over your jugular veins.